1. Field of the Invention
This invention relates to a motorized driving device for a camera, in which winding-up and rewinding of film is performed by an electric motor.
2. Description of the Prior Art
It is known to provide a motorized driving device for cameras, in which the various mechanisms of the camera including at least the film feeding mechanism are charged by an electric motor and, when the exposed film is to be rewound, the mechanism for transmitting driving torque from the motor is first changed over to a rewinding position. The motor control switch that was used when winding up is then moved again to the current supply position, as proposed, for example, in U.S. Pat. No. 4,273,432 (issued June 16, 1981). However, such conventional motorized driving device is arranged so that the motor control switch is returned to a position for operative connection with the film winding-up mechanism when changing over the transmission mechanism from the rewinding to the winding-up mode. In case the winding-up mechanism is in the charged position when such changing over operation is carried out, the current supply to the motor is stopped in response to the changing over operation. In the alternate case, where the winding-up mechanism is not yet charged, the termination of current supply to the motor is deferred until completion of charging.
That is, in such conventional motorized driving device, as the transmission mechanism is changed over from the rewinding mode to the winding mode, the current supplying state to the motor changes depending upon the position of the winding-up mechanism at the time when such changing over operation is performed. Also with the winding-up mechanism in the charged position, when the changing over operation from the rewinding mode to the winding mode is performed, it results that the motor stops at that time point.
Further, in the art of motorized driving devices for cameras, it is known to construct the transmission mechanism by using gears. But, such transmission mechanism has a problem that when changing the direction of transmission of the driving torque, it is required that after the changing over operation has been performed, the drive gear be somewhat rotated so that the phases of the teeth of the driven gear are synchronized with each other. Otherwise transmission in the reversed direction will not be established. For this reason, in such transmission mechanism, if the performance of the changeover operation from the rewinding mode to the winding mode results in suddenly stopping the motor, the transmission mechanism remains in the rewinding position.
Therefore, in the prior art motorized driving device, after the rewinding of the film had been stopped by changing over from the rewinding mode to the winding mode, when a new film was loaded into the camera and a normal winding operation was intended to take place, there was a high possibility of a full retraction of the film leader into the cartridge, as the driving torque of the motor was transmitted to the rewinding mechanism. In other words, since such prior art motorized driving device had no provision to avoid stoppage of the action of the motor upon changing over from the rewinding mode to the winding mode, there was a possibility that the direction of transmission of driving torque by the transmission mechanism remained unchanged from the rewinding mechanism side to the winding-up mechanism side, thus producing the aforesaid problem.